In many applications, semiconductor devices are packaged within a molded body for protection against the corrosive elements of the environment. A plurality of lead conductors or leads project from the sides of the molded body to electrically connect the semiconductor device to an associated circuit such as a circuit board. The lead conductors are constructed from a pliable metal which can be easily formed into a desired configuration without damaging either the semiconductor chip or the molded body. However, the application of even a small amount of pressure easily bends the leads away from the desired configuration. Considerable care must be taken when handling the packaged semiconductor device to protect the lead conductors from deformation. Even then, the leads of a large number of semiconductor devices often become deformed. For example, some leads may have been bent together, while other leads may have been bent so that the lead tips are no longer coplanar. Additionally, the lead conductors on opposing ends of the molded body may be deformed to distort the tweeze or tip-to-tip distance of the device. A semiconductor device with deformed leads is typically useless because the lead tips do not rest on the appropriate solder points and the semiconductor device does not fit within the designated location on the circuit board.
One method of mounting a semiconductor device to a circuit board includes positioning the device by hand and then soldering it in place. More commonly, the semiconductor device is set on the circuit board by an automatic placement machine, with the lead tips positioned on a spot of solder paste. The board is then heated, melting the solder paste to secure the leads in place and electrically connect the semiconductor device to other components. The tips of deformed leads often do not contact the solder paste, resulting in a defective circuit board. Moreover, the unused solder spot may bridge the pads on the board when the solder is melted, shorting the electronic circuit. Since substantial expense is involved in the manufacture of semiconductor devices, a system which would reform the bent leads to the desired configuration is desirable.
Methods exist in the art for salvaging defective semiconductor devices by straightening the bent leads. The bent lead conductors can be reformed by manually bending each lead back to the appropriate configuration. Using this method does restore many of the deformed devices to an acceptable condition, however the process is extremely time consuming and subject to human error. Additionally, the reformed leads often retain an elastic memory of the deformation and tend to partially spring back to the bent condition. If not severely deformed, the bent lead conductors may be reformed by clamping the projecting leads between opposed dies. However, clamping the lead conductors between opposed dies will not reintroduce parallelism between the leads. U.S. Pat. No. 4,727,912 shows a lead straightening device in which teeth mounted to an upper die are inserted in between the leads of a semiconductor device positioned on a lower die as the upper die is lowered. The upper and lower dies are pressed together, compressing the leads to remove elastic memory of the deformation. Although the disclosed device reintroduces parallelism between the lead conductors, severely deformed leads may be damaged by the teeth when the dies are pressed together. Moreover, the leads will spring back toward the deformed configuration since the leads retain elastic memory of the deformation. A system for reconditioning bent leads which is capable of reforming the leads while substantially erasing lead memory of prior bending is desirable.
U.S. Pat. No. 4,481,984 discloses an alternative method for conditioning the deformed leads which employs opposed blades that straighten and massage the leads as the semiconductor device passes along a track. The disclosed assembly includes a pair of wiper blades which are moved toward the semiconductor device in an arcuate path so that contact between the blades and the body of the device is avoided. After the wiper blades have been moved near the device body, the blades are lowered in a generally vertical direction to sweep the leads into grooves of a separator blade. The second wiper blade pushes the leads into the grooves and retains the leads them in place while the second wiper blade and the separator blade and the second wiper blade are oscillated, massaging the compressed leads. The disclosed assembly removes elastic memory from the deformed leads which were pressed together. However, elastic memory in the leads deformed in other ways is not completely removed and severely bent leads may be damaged as the blades are pressed together. A system for reconditioning bent leads which reintroduces parallelism and a predetermined configuration while completely erasing elastic memory of the prior deformation is desirable.
The leads of a semiconductor device are typically plated with a lead finish consisting of, for example, lead and tin. When the leads of a device are reformed, the conditioning mechanism may scrape the leads, scratching and partially removing the plated finish. A semiconductor device with scratched leads may fail to meet required quality standards, as the scratched leads may not be efficiently soldered to a circuit board. Moreover, the scratched leads often exhibit corrosion problems. The slivers produced by scraping the lead finish may accumulate in the conditioning mechanism, requiring frequent cleaning and maintenance of the lead conditioning device. A lead conditioning apparatus for reforming the bent leads of a semiconductor device which minimizes contact with the leads, and therefore scraping of the lead finish, is desirable.
Semiconductor devices produced by different manufacturers often have different dimensions, particularly if the devices are produced in different countries. Many lead conditioning systems will not accommodate the dimensional variations of devices produced in different countries. Thus, when semiconductor devices from several manufacturers are employed, multiple lead conditioning systems may be required for conditioning and reforming bent leads. A lead conditioning system which may be conveniently adjusted so that variations among different semiconductor devices may be accommodated is desirable.
The disclosed assemblies may be employed to reform leads projecting from only one or two sides of a semiconductor device. A system which efficiently and conveniently reconditions leads projecting from all four sides of a semiconductor device simultaneously would be particularly valuable.